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Agriculture
Canada

■ * y Agriculture

Canada

MAR 3 0 !993

Library / Bibliotheque, Ottawa K1A 0C5

Research Branch
Technical Bulletin 1 992-8E

Fall compared

to spring

application of

nitrogen

fertilizers in

Alberta

Canada

Cover illustration

The images represent the Research Branch's objective:

to improve the long-term competitiveness of the Canadian

agri-food sector through the development and transfer of new.

technologies.

Illustration de la couverture

Les dessins illustrent l'objectif de la Direction generate de la

recherche : ameliorer la competitivite a long terme du secteur

agro-alimentaire canadien grace aia mise au point et au transfer!

de nouvelles technologies.

Conception par le Service aux programmes de recherches.

Fall compared to
spring application of
nitrogen fertilizers in

Alberta

S.SMALHI

Agriculture Canada

Research Station

Lacombe, Alberta

M. NYBORG

Department of Soil Science

University of Alberta

Edmonton, Alberta

E.D. SOLBERG, DJ. HEANEY

Soils Branch

Alberta Agriculture

Edmonton, Alberta

Technical Bulletin 1992-8E

Research Branch

Agriculture Canada

1992

Copies of this publication are available from

Director

Research Station

Research Branch, Agriculture Canada

Bag Service 5000

58th SL at the C & E Trail

Lacombe, Alberta

T0C1S0

Egalement disponible en francais sous le titre
Comparaison des applications automnales et
printaniires d'engrais azotis en Alberta

CONTENTS

ACKNOWLEDGEMENTS iv

SUMMARY / RESUME v

INTRODUCTION 1

REASONS FOR INFERIORITY OF FALL- APPLIED N 1

FACTORS AFFECTING EFFICIENCY OF FALL- AND SPRING- APPLIED N 3

Kind of N Fertilizer 3

Date of Fall Application 4

Inhibitors and Slow-Release N Fertilizers 7

Methods of N Placement 7

Depth of Placement of Spring-Applied N 11

Rate of N, Soil Test N03-N and Yield Response 11

Texture, Drainage and Fall Soil Moisture 12

Soil-Climatic Zone. 12

CONCLUSIONS. 13

RECOMMENDATIONS. 15

REFERENCES 16

ACKNOWLEDGMENTS

The authors thank the Agricultural Research Council of Alberta (Farming for the
Future Program), Alberta Agriculture Research Trust, Western Co-operative Fertilizers
Limited and the Sulphur Institute for financial support. Acknowledgment is given to
Alberta Agriculture Soils and Animal Nutrition Laboratory for certain analyses.

SUMMARY

In Alberta and other Prairie Provinces, fall-applied N is often less effective than
spring-applied N. The study was conducted to find reasons for inferiority of fall-applied
N, and to determine the effect of various factors on the relative effectiveness of fall-
versus spring-applied N and to investigate methods to improve the efficiency of fall-
applied N. The poor performance of fall-applied urea was attributed to nitrification over
the winter and subsequent denitrification in early spring after the snow melt. The loss of
fall-applied N from mineral N pool was also caused by immobilization. The effectiveness
of fall-applied N was improved by using ammonium-based fertilizers, delaying application
in fall, and placing N fertilizer in widely-spaced bands and more so in nests or as large
pellets. Inhibitors were also effective in increasing yield response of barley to fall-applied
N, but may not be cost-effective. The relative efficiency of fall- versus spring-applied N
was also increased with increasing N rate and soil test NO3-N level, fine texture, better
drainage, drier soil conditions in fall and spring, and from Grey Luvisolic soil zone in
northern to Brown soil zone in southern Alberta.

RESUME

En Alberta, tout comme dans les autres provinces des prairies, la fumure azotee appliquee
en automne est souvent moins efficace que celle appliquee au printemps. Cette 6tude a ete
entreprise pour en determiner les raisons et pour comparer l'effet de certains facteurs sur
refficacite" de l'application de fumure azot6e automnale et printaniere et pour examiner des
methodes qui pourraient ameliorer le rendement de la fumure azot6e automnale. La faible
production associee a l'epandage d'uree automnale a €i€ attribute a une nitrification durant
l'hiver suivie d'une denitrification apres la fonte des neiges. La perte de fumure azotee
automnale du pool d'azote inorganique a aussi ete causee par immobilisation. On a
ameliore l'application de fumure azotee automnale grace entre autres a l'utilisation de
fertilisants a base d'ammonium, en retardant l'application plus tard a l'automne et en
pla?ant un fertilisant a large granulomere, en bandes bien espacees. Des inhibiteurs ont
accru le rendement de l'orge sur fumure azotee automnale meme s'ils peuvent s'averer non-
rentables. On a 6galement ameliore refficacite relative de la fumure azotee automnale, en
augmentant la teneur d'azote et d'azote nitrique du sol, avec une texture plus fine, un
meilleur drainage, des conditions de sol plus sec a l'automne et au printemps et ce, de la
zone des sols luvisoliques gris au nord de la province jusqu'a la zone des sols bruns au sud.

INTRODUCTION

In Alberta, and the other Prairie Provinces, nitrogen (N) fertilizers are often applied in
fall rather than in spring for spring-sown crops. Fertilizing with N in the fall, rather than in the
spring, has two main advantages - lower fertilizer prices and convenience. The main
disadvantage is that yield increases from fall application can be considerably lower than those
obtained from spring application (Table 1). The effectiveness of fall-applied N as compared to
spring-applied N can be influenced by a number of factors. Management factors include: kind
of N fertilizer, date of fall application, method of placement, use of nitrification inhibitors and
slow-release N fertilizers, and straw handling. Other factors are: soil texture, drainage, fall soil
moisture, soil-climatic zone, depth of placement and early growing season precipitation; rate of
N, soil test nitrate-N level and yield response to applied N. This bulletin contains information
for fertilizer dealers, agricultural extension personnel and farmers on the effect of these factors
on the effectiveness of fall- versus spring-applied N. The information is based on field
experiments, most of which were conducted in central and north-central Alberta.

Table 1 Yield increase and N uptake of barley grain from fall and spring applications of urea
incorporated into soil at 56 kg N/ha (average of 44 experiments)

Time of N application Relative

Measurement Fall Spring efficiency^

Increase in grain 970 1840 55

yield (kg/ha)

% recovery of 27 55 50

applied N in grain

^Relative efficiency was calculated as yield increase from fall-applied N, divided by yield increase from spring-
applied N and multiplied by 100.

REASONS FOR INFERIORITY OF FALL-APPLIED N

Soil sampling of fall-fertilized plots from fall through winter has shown that fall
incorporated urea slowly forms nitrate (nitrification) over the winter, even when soils are frozen
(Table 2). Nitrate is subject to loss by denitrification (formation of nitrogen gases) when soil is
wet and poorly aerated. In a number of experiments, early spring recovery of ^N-tagged1 fall-
applied N in soil was very low and the amount recovered was highly dependent on the kind of
fertilizer applied (Table 3 and Fig. 1). Nitrogen loss was much greater from nitrate-based
fertilizer than from ammonium-based fertilizer. Early spring N loss was primarily due to

1 ^N is a heavy isotope of N that researchers use to track fertilizer N through the soil and plant.
This provides an easy accounting of N applied.

denitrification rather than leaching. Fall-applied N had not moved below the 60 cm depth
(Table 3). Similar experiments with 15N-tagged N indicate nitrate losses take place during
episodes of mild weather in winter and during spring thaw whenever snow melts and the soil is
wet.

Table 2 Apparent nitrification of applied N during winter, after incorporation of urea at 56 kg
N/ha on 6 October (average of 6 experiments)

Fertilizer^
treatment

% of applied urea N found as nitrate-N

21 Oct.

7 Dec.

6 Mar.

Urea - incorporated

Urea - banded

U+I - incorporated

U+I - banded

§ U+I refers to urea + inhibitor pelleted together in a ratio of 2:1, respectively.

Table 3 The recovery of fall-applied 15N-labelled fertilizers applied in October or December at
1 12 kg N/ha from the soil N in the following May

Percent recovery (

>f 15N-labelled fall-applied

Soil

Average

of two experiments

Average of three experiments

depth
(cm)

KNO^

(incorp.)§

Urea
(incorp.)

(NH4)2S04
(banded)

KNO^

(banded)

(NH4)2S04
(banded)

(NH4)2S04 +
thiourea (banded)

0-15

15-30

30-60

60-90

90-120
Total

0
63

0
94

0
98

^Incorporated.

100
90
80
70
60
50
40

O 30

20 -

ffl

Application Date: Q8ct £l^ Jun.
Year.
Source:
Site:

8 26 v i
Oct. Oct .Mar. Jun.

1982 I 1983 1982 I 1983

Urea KN03

Breton

"] Losses by spring

J Losses from spring until tall

J S.E. for spring loss

I S.E. for spring loss plus
spring to fall loss

ffl

8 26 23 20

Oct. Oct.iFeb May

1982 I 1983

Urea

8 26 23 20

Oct. Oct .Feb May

1982 I 1983

KNO3

Innisfail

Fig. 1. Loss of "N from soil at sowing and from soil and plants at harvest, with four dates of application for
each fertilizer and site.

FACTORS AFFECTING EFFICIENCY OF FALL- AND SPRING-APPLIED N
Kind of N Fertilizer

In a series of experiments, calcium nitrate and urea were incorporated into soil in the fall
and average yields were lower with calcium nitrate than urea (Table 4). In four experiments
comparing fall application of ammonium sulphate with urea, ammonium sulphate produced
greater yields. In another four experiments, fall-applied ammonium nitrate yielded slightly less
than fall-applied urea. These three sets of comparisons (Table 4) indicate that nitrate-based
fertilizers are often inferior to ammonium-based fertilizers when applied in the fall.

Table 4 Yield increase and N uptake of barley grain with fall and spring incorporation
applications of N fertilizers at 56 kg N/ha in field experiments

Increase in

% recovery

Relative

grain yield

of applied N

efficiency

efficiency (N

No. of tests

Treatment^

(kg/ha)

in grain

(Yield)t

recovery)t

CN-fall

802

Urea-fall

940

Urea-spring

1683

AS-fall

1435

Urea-fall

1130

Urea-spring

2335

AN-fall

750

Urea-fall

848

Urea-spring

1285

§CN, AS and AN refer to calcium nitrate, ammonium sulphate and ammonium nitrate, respectively.
^Relative efficiency was calculated as yield increase (or N recovery) from fall-applied N, divided by yield
increase (or N recovery) from spring-applied N and multiplied by 100.

Date of Fall Application

Nitrification rates in soil are positively correlated to soil temperature. As a result,
conversion of added ammonium to nitrate should be greater with early fall when soils are warm
than with late fall application when soils are cool. Soil temperature steadily decreases from mid-
September to early November when the soil begins to freeze (Figure 2). One would thus expect
more over-winter loss of fall-applied N and subsequently lower N uptake and yield of the crop,
with the application of ammonium fertilizers in early as compared to late fall. To investigate
this scenario, 15 experiments were conducted in which urea was broadcast and incorporated at 2
or 3 dates in the fall. The recovery of mineral N (ammonium plus nitrate) in the spring was
greater when applications were made in late fall as compared to early fall (Figure 3). The %
recovery of fall-applied N as soil mineral N found in spring increased from 31% with urea added
on 20 September to 73% with urea applied on 31 October (based on the linear regression).

Fall incorporated urea produced less barley yield relative to urea applied in the spring
(Figure 4). Delaying application in the fall markedly improved yield response. Yield increase
from fall-applied N as a % of yield increase from spring-applied N rose from 23% for urea

CD
Z3
03

O
CO

16
14

12
10
8
6
4
2
0-
-2
-4
12
10
8
6
4
2
0
-2

110

Lacombe

Ellerslie

Sept. 15 Sept. 30 Oct. 15
Date

Oct. 30 Nov. 14

100

Q.
V)

o
o

CD
0C

Co* relator cocfltctenl ('):0 M"
Y = »0t •* to?*

WhC'e X - Nwmbet O* OJ-yi •"— '--(- IS

S 50

0 15 30 45 60

Sept. IS Sept 30 Oct. 1S Oct 30 Nov. 14

Date of Fall Application

Fig. 2 Mean daily soil temperature in the morning (6 or 8 h) and the Fig. 3 Effect of date of N application in fall on the recovery of

afternoon (17 or 18 h) at 5 cm depth at meteorological stations applied N as mineral N in soil in spring from urea at N rates of

in Ellerslie (northcentral Alberta) and Lacombe (central 50 or 56 kg/ha.
Alberta), averaged from 1975 to 1984

100

z 90
■D

a 80

<D
</)
CO

£ SOF-

TS
oj
>

J2 10

Correlation coeHicieni (r)=068"

¥ = UB < 1 09K
Where X - Nunttef o) day* aiw* Sccn IS
Y = RHaii<>« y«*d «nc«ease ot
Fan* vfw Sprtng-appfccd N

Sept. 15

15
Sept 30

30
Oct 15

45
Oct. 30

Nov 14

TO
O

IUU

Correlation coetlicienl <r)=066"

X =

17« « 1BSX

Where

x =

Number o* dan atler Sept IS

Y =

Relative % N wee— y of
Fan- wertui Sprtng-apphed N

•
•

•

•
*•

• /

•
•

•

• /

m/ «i

•/

• /

•

• /

/ *
/ *

•

• •

•

1 1

Date of Fall Application

0 15 30 45 60

Sept. 15 Sept 30 Oct 15 Oct 30 Nov. 14

Date of Fall Application

Fig. 4 Effect of dale of N application in fall on relative yield increase Fig. 5 Effect of date of N application in fall on N uptake in barley
of barley grain from fall- versus spring-applied urea at N rates grain from fall-applied urea relative to spring-applied urea at

of 50 or 56 kg/ha. N rates of 50 or 56 kg/ha.

Table 5 The recovery of applied N as ammonium-N and mineral N in soil (0-90 cm) in May,
yield increase and N uptake of barley grain with the application of urea and U+I§ (2:1) in
October at 56 kg N/ha (average of 10 field experiments)

N applied

in fall

N applied
Urea-

in spring

Urea-

U+I-

Urea-

Parameter

Incorp.t

Banded

Incorp.t

Banded

Incorp.t

Banded

% recovery in soil as

ammonium-N

% recovery in soil as
mineral N

Increase in grain yield
(kg/ha)

1070

1250

1440

1740

2000

2090

% recovery of applied N

in grain

»U+I (2:1) refers to urea + inhibitor pelleted together in a ratio of 2:1, respectively. Thiorea is a nitrification

inhibitor.

t Incorporated.

Table 6 Grain yield increase and % recovery of applied N in grain and in soil in spring from
urea solution and aqua NH3 with and without inhibitors banded in fall and spring (average of 6
experiments for aqua NH3 and 10 experiments for solution urea)

Yield
increase
(kg/ha)

% recovery of applied Is

Fertilizer

In grain

In soil (0-30

cm)

treatment^

Ammonium-N

Mineral N

Aqua NHrfall

763

Aqua NH3 + Inhibitors ■

■fall

1144

Aqua NH^-spring

1557

Urea-fall

972

Urea + Inhibitors - fall

1358

Urea-spring

1853

^Inhibitors used were ATC, N-Serve 24E, CS2, (NH4)2CS3, K2CS3 and thiourea applied at 2, 4, 10, 20, 24 and
45 kg/ha, respectively.

applied on 20 September to 69% for urea applied on 31 October. The values of N uptake by
barley showed similar pattern to yield increase values (Figure 5). The N uptake was greater
with late fall compared to early fall application.

The efficiency of fall incorporated urea as compared to spring incorporated urea varied
greatly from experiment to experiment. This is not unexpected as the experiments were
conducted on a variety of soils over a number of years. Nevertheless, early fall application for
barley was inefficient while application in late fall at times achieved efficiencies close to spring
application (Figures 4 and 5). Keep in mind, however, that these experiments used incorporated
urea. Banding which tends to increase the efficiency of fall application, may be less sensitive to
application date.

Inhibitors and Slow Release N Fertilizers

Ammonium can neither easily leach from soil nor is it subject to denitrification in soil.
Nitrate can be lost through both mechanisms. Inhibitors, which suppress the formation of nitrate
from ammonium-based fertilizers, should reduce over-winter loss of fall-applied N and increase
crop yield. A number of inhibitors (thiourea, ATC, N-Serve 24E, CS2, (NH4)2 CS3 and K2CS3)
were tested with urea or aqueous NH3. These inhibitors were all effective in suppressing
nitrification of fall-applied N (Tables 2, 5 and 6) and in reducing over-winter N losses,
especially when the N fertilizer plus inhibitor were placed in bands (Tables 5 and 6). In most
cases, these reduced losses translated into substantial increases in barley yield (Tables 5 and 6).
However, placing fertilizer in concentrated bands or nests was equal or better than the inhibitors
(see section on Methods of N Placement).

This research tested only one slow-release N fertilizer, sulphur-coated urea (SCU).
Sulphur-coated urea was not effective in improving the effectiveness of fall-applied N and it
gave poor barley yields when applied in the spring. The explanation was that N release from
SCU was too slow to meet the crop needs.

Methods of N Placement

Nitrification inhibitors were effective in improving barley yield response to fall-applied
N. However, they may not be convenient to apply with N fertilizers or cost-effective. In
addition, many of the inhibitors were found to slow the release of mineral N from native soil N.
Therefore, field experiments were conducted to find if the effectiveness of fall-applied urea
could be improved by concentrating the fertilizer through placement in bands, and in nests or as
large pellets.

Yield and recovery of applied N in barley grain were considerably lower with fall
application than spring application in four experiments comparing broadcast, incorporated and
banded (22.5 cm spacing) applications (Table 7). Overall, broadcast application was least
effective and band placement was most effective. Nevertheless, yields with fall banding were
still inferior to those with spring banding.

Experiments were conducted with further concentration of urea or aqua NH3 by placing
in widely-spaced bands (45 cm spacing) or in nests or as large pellets. The nest method of
application was performed by placing a number of commercial fertilizer granules at a point

Table 7 Yield increase and % recovery of applied N in barley grain with fall and spring
applications of urea at 56 kg N/ha following different methods of placement (average of 4
experiments)

Fall-applied N Spring-applied N

Parameter Broadcast^ Incorp.t Banded* Broadcast Incorp.t Banded

Increase in grain
yield (kg/ha)

% recovery of
applied N in grain

543 848 1018 998 1285 1425

18 27 33 31 41 46

§ Surface broadcast.

t Incorporation.

tBands were 22.5 cm apart.

below the soil surface. For the large pellet method, urea pellets ranged from 1- to 3-g weights.
Single pellets were placed below the surface on a fixed grid. Grid spacings increased with pellet
size in order to give the same N rate in all treatments. The main purpose of bands, nests or
pellets is to keep the fall-applied N in ammonium form by reducing the contact area between
fertilizer and soil.

Almost all of the fall-applied incorporated urea granules nitrified by May (Table 8). The
recovery of applied N as NH4-N increased markedly when the fertilizer was banded or nested.
The recovery of applied N in mineral N was also much greater with banding and even greater
with nesting than mixing, indicating that over-winter N losses were reduced substantially when
urea was placed in bands or nests. Yield and recovery of applied N in grain was also improved
(Table 8). The barley yields with nests of urea were very close to those obtained with spring-
applied N. The results were similar with aqua NH3 placed in bands or nests. In a few
experiments, nitrification inhibitors were used with nest placement, but there was no further
improvement in crop yield from the use of inhibitors.

When straw is returned to the field, it tends to temporarily immobilize N and can affect
the amount of fertilizer N available for the next crop. Two field experiments investigated
whether or not the effect of straw can be minimized by placing N fertilizer in bands or in nests
or as large pellets. For fall-applied N, placing urea in nests improved barley yields and N use
efficiency in both straw-off and straw-on treatments, though yields were slightly lower when
straw was retained than when it was removed (Table 9). With spring-applied N, the yield
difference between straw-off and straw-on plots was 625 kg/ha for the incorporation application
and only 190 kg/ha when the fertilizer was banded at sowing. Apparently, less of the applied N
will be immobilized in the soil organic matter as shown by the ^N experiments (Table 10).
This leaves more fertilizer N for crop uptake.

Table 8 Effect of method of placement on yield increase and % recovery of applied N in grain
and in soil in May from urea applied at 50 or 56 kg N/ha in the fall and in the spring (average of
20 experiments)

Yield
increase
(kg/ha)

% recovery of applied N

Fertilizer

In grain

In soil

(0-

60 cm)

treatment^

NH4-N

Mineral N

Urea incorp.t-fall

839

Urea banded-fall

1238(950)

36(26)$

20(16)

66(52)

Urea nested-fall

1509(1535)

46(45)

50(36)

77(84)

Urea incorp.t-spring

1644(1763)

51(54)

§Bands were 45 cm apart. In 7 experiments urea nested was 2-g, or 2.5-g pellets.

t Incorporation.

tin brackets are the results with aqua NH3 in four experiments.

These experiments indicate that banding and nest placement or large urea granules are
good alternative to chemical nitrification inhibitors for conserving fall-applied N both from
economical and environmental point of view. Use of concentrated placement in bands or nests
allows effecient production, reduces the potential of environmental impact from nitrate leaching
and denitrification and incurs no added chemical expenses.

Six field experiments were conducted to answer the question of whether or not large urea
pellets are as effective as commercial urea when applied in spring. Urea placed in nests or as
large pellets (2-g or larger) at sowing was much less effective in increasing barley yield than
commercial urea incorporated into the soil just prior to sowing or side banded at sowing
(average yield increase was 853 kg/ha for large urea pellets and 1517 kg/ha for commercial
urea). In one experiment, yield response to applied N decreased from 1240 kg/ha with 1-g
pellets to 490 kg/ha with 3-g pellets. The main reason for this poor performance of large pellets
applied in spring was the slow diffusion of N from the pellet to the plant roots and essentially the
fertilizer N in pellets becomes isolated from many of the growing plants for a period of time in
the early peak growing season.

In the Prairie Provinces, denitrification of spring-applied N fertilizers (as opposed to fall-
applied N) is not a serious problem in most years. Thus spring-applied nest or large pellets are
of no particular advantage. Any risk of N loss from spring-applied N can be easily overcome by
banding and does not need the use of large pellets.

Table 9 Influence of disposal of straw of the previous crop and method of N placement on grain
yield of barley and N use efficiency with fall and spring application of urea at 50 kg N/ha
(average of 2 experiments)

Grain yield (kg/ha)
Straw-Off Straw-On

N use efficiency

(kg grain/kg N)

Straw-Off Straw-On

%
of

recovery
applied N

Fertilizer treatment^

Straw-Off Straw-On

Control

2065

1665

Urea incorp.t-fall

2815

2740

15.0

21.5

Urea banded-fall

3210

2815

22.9

23.0

Urea pellets-fall

3300

3105

24.7

28.8

Urea incorp.t-spring

3435

2810

27.4

22.9

Urea-banded-spring

3460

3270

27.9

32.1

§Fall bands were 45 cm apart. Pellets contained 2-g of urea. In spring urea was banded 4 cm beside and below

the seed row.

'Incorporation.

Table 10 Influence of method of placement and straw addition on the recovery of 15N-labelled
urea applied at 50 kg N/ha at sowing, in barley plants and soil at harvest

Method of
placement

% recovery

of applied N

plants

In soil

Location

Without
straw

With
straw

Without
straw

With
straw

Rimbey
Ellerslie

Incorp.§
Banded

Nested

Incorp.§
Banded

Nested

60.1
73.9
76.0

11.8
27.1
50.8

51.7
71.0
77.8

13.8
27.6
46.6

29.9
18.8
15.8

36.4
22.0
22.0

36.9

21.2
20.7

48.9
26.9
26.9

^Incorporation.

Depth of Placement of Spring-Applied N

The availability of fertilizer N to the crop can be affected by its position in relation to
plant roots. Under dryland conditions the upper most layer of soil generally dries out early in
the cropping season. Roots near the surface become inactive and do not take up nutrients. As a
result, fertilizer is "stranded" in this dry surface layer (J.T. Harapiak-Personal Communication).
Furthermore, N fertilizer, especially urea, at or near the surface is vulnerable to loss through
ammonia volatilization. This can limit crop response to the applied N. Field experiments were
conducted to study the effects depth of N fertilizer placement on crop growth (Table 11). In
four experiments (No. 18-21), the yield benefit of urea incorporated to a depth of 10-12 cm over
surface-applied urea amounted to 290 kg/ha, while the advantage of banding over surface-
applied urea was 430 kg/ha.

In another experiment (No. 8), grain yield was much higher for deeper incorporation and
for deeper banding as compared to shallow incorporation or banding. In this experiment, depth
of shallow incorporation or shallow banding was not more than 4 cm and surface soil was very
dry during the early part of the growing season. In the shallow incorporation treatment, it is
likely that the fertilizer N was "stranded" near the surface and was not available to plants early in
the growing season. In the other experiments under more favourable moisture conditions, there
were little or no differences in yield between shallow and deep placements.

These results indicate that the response to applied N can be modified by the depth at
which the fertilizer is applied. The advantage of deep placements over shallow placement
appears to be offset if rainfall occurs soon after fertilizer application. The advantage is likely to
be greater during relatively dry years when the fertilizer is "stranded" during the key early
growth stages. This lower yield with shallow spring-applied N can mask the relative difference
between fall- and spring-applied N.

Rate of N, Soil Test NO3-N Level and Yield Response

In general, the yield response to each additional increment of applied N normally
decreases with increasing rate of N. Therefore, one would expect smaller relative yield
difference between fall- versus spring-applied N (relatively) when the rate of fertilizer is high.
Eight field experiments were conducted to determine the effect of rate of urea N on the relative
efficiency of fall- versus spring-applied N (Table 12). The differences between fall- and spring-
applied N for N use efficiency and % N recovery of applied N decreased, as N rate increased.
The relative efficiency of fall- versus spring-applied urea increased from 47 to 73% when the N
rate was increased from 25 to 100 kg N/ha. This does not imply that high N rates reduce over-
winter loss, but instead they mask the differences between fall and spring-applied N. The use of
extra N fertilizer to compensate for the over-winter N loss is neither an economical nor an
environmentally sound practice. Other techniques such as banding or nesting or large pellets
should be used to improve the effectiveness of fall-applied N.

Table 1 1 Effect of depth of placement of urea, on grain yield of barley, applied at time of
sowing in 33 field experiments in central and north-central Alberta

Control

Shallow-

tilled§

Control
Deep-
tilled§

Yield of barley

grain (kg/ha)

Experiment
number

Urea
Shallow-
tilled
Shallow-
incorporated

Urea
Deep-tilled

Deep-
incorporated

Urea
Shallow-
tilled
Shallow-
banded

Urea

Deep-tilled

Deep-banded

1-4

2020

2860

3880

3890

5-7

1960

1980

2930

2880

3160

3180

mot

2100

1790t

3090

2460

3390

9-17

1520

3750

3830

18-21

1100

2090*

2380

2520

22-33

1900

2740

2770

§Shallow-tilled (5 to 7 cm depth) and Deep-tilled (10 to 12 cm depth).

^The plots were tilled to a depth of less than 4 cm.

+Urea was broadcast and not incorporated into soil in these experiments.

Yield response to fertilizer N also decreases with increasing levels of plant-available N in
soil. In our work in central Alberta, there was little response to fall- or spring-applied N on soils
with large amounts of NO3-N as compared to soils with low levels of NO3-N (data not shown).

Texture, Drainage and Fall Soil Moisture

To determine the effect of soil conditions on the relative efficiency of fall- versus spring-
applied urea, field sites were separated by texture, drainage and wetness of soil in the fall (Table
13). The sites with imperfect drainage, soil moisture above field capacity in fall and coarse to
medium texture tended to show lower relative efficiency of N use than the sites with good to
moderate drainage, soil moisture below field capacity in fall and fine to very fine texture.

Soil-Climatic Zone

Laboratory incubation studies showed that soils in all agro-climatic zones in Alberta have
similar potentials for NO3-N loss under anaerobic conditions (Table 14), but the actual loss from
fall-applied N in the field depends on soil-climatic conditions. The Brown and Dark Brown soil
zones are relatively dry and soils seldom become water saturated during the spring thaw. While

Table 12 Effect of N rate on N use efficiency, % recovery of applied N in grain and relative
efficiency of fall- versus spring-applied urea (average of 8 experiments)

Rate of N
(kg N/ha)

Time of
application

N use

efficiency

(kg of grain

/kg of N)

% recovery
of applied
N in grain

Relative

efficiency

(yield)§

Relative

efficiency

(N recovery)^

Fall

15.7

20.0

Spring

34.1

48.9

Fall

16.6

25.8

Spring

28.9

43.7

100

Fall

15.8

27.1

Spring

20.0

34.9

^Relative efficiency was calculated as yield increase (or N recovery) from fall-applied N, divided by yield
increase (or N recovery) from spring-applied N and multiplied by 100.

Black and Gray Luvisolic zones are relatively moist and soils are usually water saturated for
several days after the snow thaw. Field experiments using 15N-labelled KNO3 were carried out
from Beaverlodge in northern Alberta to Lefhbridge in southern Alberta to determine the over-
winter loss of winter-applied N in various soil zones of Alberta (Table 14). The over-winter loss
of applied N was much greater in the central and northern portions than in the southern portions
of Alberta. However, these experiments were conducted only one year and the values given in
Table 14 would differ in other years depending on localized climatic conditions.

The results of 99 field experiments were summarized to compare the yield response of
barley or wheat to fall- versus spring-applied urea incorporated into soil in different soil zones in
Alberta (Table 15). The relative efficiency of fall-versus spring-applied N was lower in the
Gray Luvisol and Black soil zones as compared to Dark Brown and Brown soils zones.

CONCLUSIONS

Fall-applied N was inferior to spring-applied N because of substantial over-winter
nitrification and subsequent N loss in early spring through denitrification. Over-winter N loss
was greater from nitrate than from ammonium, and ammonium-based fertilizers were more
effective than nitrate-based fertilizers in increasing yield of barley.

The effectiveness of fall-applied N was greatly improved by placing urea in widely-
spaced bands and more so by placement in nests or as large pellets. This increased effectiveness

Table 13 Effect of factors on the yield increase and N recovery of fall versus spring applications
of urea at 56 kg N/ha in 44 field experiments

Relative

Relative efficiency

Factors

No. of expts.

efficiency (Yield)§

recovery)^

Texture

Coarse to medium

Fine to very fine

Drainage

Well to mod. well

Imperfect

Fall moisture

<75%ofFCt

75 to 100% FC

>FC

^Relative efficiency was calculated as yield increase (or N recovery) from fall-applied N, divided by yield
increase (or N recovery) from spring-applied N and multipled by 100.
^FC (field capacity) refers to moisture content in soil at 33 kPa.

Table 14. Denitrification potential and actual over-winter N loss from winter-applied 15N-
labelled KNO3 in soils from northern to southern Alberta

Denitrification

potential

% of winter-applied

Location

Area of Alberta

(mg N/kg soil/day)

Nlost

over the winter

Beaverlodge

Northern

Ellerslie

North-central

Rim bey

Central

Calgary

South-central

Granum -Vauxhall

Southern

Table 15 The relative efficiency of fall- versus spring-incorporated§ N in various soil zones t

Soil zone

No.

of sites

Relative

efficiency

(Yield)*

No.

of sites

Relative
efficiency

(N recovery)!

Luvisolic

Black

Dark Brown

Brown

§The N fertilizer was incorporated to a depth of 5 to 7 cm in most of the experiments in the Brown and Dark

Brown soil zones and about one-third of the experiments in the Luvisolic and Black soil zones, and to a depth of

10 cm in other experiments,
t Relative efficiency was calculated as yield increase (or N recovery) from fall-applied N, divided by yield

increase (or N uptake) from spring-applied N and multiplied by 100.
^Source - Bole et al. 1984. Regional and environmental influence on N use efficiency. Pages 1-29 in Proc.

Alberta Soil Science Workshop, 21-22 Feb. 1984, Edmonton, Alberta.

was due to slower nitrification and possibly reduced immobilization of applied N by banding or
nesting as compared to incorporation. Surface-broadcasting was least effective. Delaying urea
application in fall until close to freeze-up also improved the efficiency of fall-applied N. Spring
application of urea in nests or as large pellets reduced yield response because the fertilizer
becomes spatially unavailable to plants for a period of time in early peak growing season.

Inhibitors were effective in slowing nitrification, reducing over- winter N loss and
improving yield response of barley to fall-applied N. However, inhibitors may be inconvenient
to apply and may not be cost-effective. Sulphur-coated urea (a slow-release fertilizer) was not
effective in improving the efficiency of fall- or spring-applied N.

The relative efficiency of fall- versus spring-applied N increased with increasing N rate,
increasing soil test NO3-N level, finer texture, better drainage, and drier soil conditions in fall
and early spring. Over-winter N loss was greatest in the Gray Luvisolic soil zone and least in
the Brown soil zone.

RECOMMENDATIONS

1. Use ammonium-based N fertilizers for fall application.

2. Apply N fertilizer in widely-spaced bands below the soil surface or use any other
fertilizer application technique which reduces soil-fertilizer contact.

3. Delay fall application to as close to freeze-up as possible.

4. For maximum benefit from spring-applied N, incorporate N fertilizer to a depth of 10-12

cm or band below seeding depth.

REFERENCES

Bole, J.B.; Harapiak, J.T.; Malhi, S.S.; Penney, D.C. 1984. Regional and environmental
influence on nitrogen use efficiency. In Proceedings of Alberta Soil Science Workshop,
pp. 1-18.

Heaney, D.G.; Blades, A.T.; Malhi, S.S.; Nyborg, M. 1984. Over-winter mineralization,
immobilization and denitrification of mineral nitrogen. In Proceedings of Alberta Soil
Science Workshop, pp. 46-59.

Heaney, D.J.; Nyborg, M.; Solberg, E.D.; Malhi, S.S.; Ashworth, J. 1992. Overwinter nitrate
loss and denitrification potential of cultivated soils in Alberta. Soil Biol. Biochem. 24:

877-884.

Malhi, S.S.; McGill, W.B. 1982. Effect of temperature, moisture, and substrate concentration on
the rate of nitrification. Soil Biol. Biochem. 14:393-399.

Malhi, S.S.; Nyborg, M. 1979. Nitrate formation during winter from fall-applied urea. Soil
Biol. Biochem. 11:439-441.

Malhi, S.S.; Nyborg, M. 1982. An evaluation of carbon disulphide as a sulphur fertilizer and as
a nitrification inhibitor. Plant and Soil 65:203-218.

Malhi, S.S.; Nyborg, M. 1983. Field study of the fate of fall-applied 15N in three Alberta soils.
Agron. J. 75:71-74.

Malhi, S.S.; Nyborg, M. 1983. Release of mineral N from soils: Influence of inhibitors of
nitrification. Soil Biol. Biochem. 15:581-585.

Malhi, S.S.; Nyborg, M. 1984. Inhibiting nitrification and increasing yield of barley by band
placement of thiourea with fall-applied urea. Plant and Soil 77: 193-206.

Malhi, S.S.; Nyborg, M. 1984. Methods of placement for increasing the efficiency of N
fertilizers applied in the fall. Agron. J. 77:27-32.

Malhi, S.S.; Nyborg, M. 1986. Increase in mineral N in soils during winter and loss of mineral
N during early spring in north-central Alberta. Can. J. Soil Sci. 66:397-409.

Malhi, S.S.; Nyborg, M. 1988. Effect of ATC, N-Serve 24E and thiourea nitrification inhibitors
on yield and N uptake of barley fertilized with fall-applied N. Plant Soil 105:223-229.

Malhi, S.S.; Nyborg, M. 1988. Control of nitrification of fertilizer nitrogen: Effect of inhibitors,
banding and nesting. Plant Soil 107:245-250.

Malhi, S.S.; Nyborg, M. 1990. Efficiency of fall-applied urea for barley: Influence of date of
application. Fert. Res. 22:141-145.

Malhi, S.S.: Nyborg, M. 1991. Recovery of 15N-labelled urea: Influence of zero tillage, and
time and method of application. Fert. Res. 28:263-269.

Malhi, S.S.; McGill, W.B.; Nyborg, M. 1990. Nitrate losses in soils: Effect of temperature,
moisture and substrate concentration. Soil Biol. Biochem. 22:733-737.

Malhi, S.S.; Nyborg, M. 1992. Fall- versus spring-applied urea: Influence of N rate. Commun.
Soil Sci. Plant Anal. 23: 301-312.

Malhi, S.S.; Nyborg, M.; Solberg, E.D. 1989. Recovery of 15N-labelled urea as influenced by
straw addition and method of placement. Can. J. Soil Sci. 69:543-550.

Monreal, C. 1981. Nest placement of nitrogen fertilizers. M.Sc. Thesis. University of Alberta,
Edmonton, Canada.

Nuttal, W.S.; Dawley, W.K.; Malhi, S.S.; Bowren, K.E. 1989. The effect of spring and fall
application of N on yield and quality of barley (Hordeum vulgar e L.) and rapeseed
{Brassica campestris L.). Can. J. Soil Sci. 69:199-211.

Nyborg, M.; Malhi, S.S. 1979. Increasing the efficiency of fall-applied urea fertilizer by placing
in big pellets or in nests. Plant and Soil 52:461-465.

Nyborg, M.; Malhi, S.S. 1986. Comparison of fall and spring application of nitrogen fertilizers
in northern and central Alberta. Can. J. Soil Sci. 66:225-236.

Nyborg, M.; Malhi, S.S.; Solberg, E.D. 1990. Effect of date of application on the fate of 15N-
labelled urea and potassium nitrate. Can. J. Soil Sci. 70:21-31.

Nyborg, M.; Malhi S.S. 1992. Effectiveness of fall-versus spring-applied urea on barley: Pellet
size and depth of placement. Fert. Res. 31: 235-239.

3 ^073 000^S33T 0

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